In general, a hydraulic machine such as an actuator and the like to be hydraulically driven and controlled is supplied with working oil through pipes. The actuator of this type to be hydraulically driven and controlled is for example mounted on a vehicle like an automotive vehicle, and thus utilized for controlling a wide variety of drive units provided on the vehicle.
As an apparatus for braking a vehicle provided with a hydraulic machine such as an actuator and the like, there has so far been known a brake system which comprises a master cylinder to be operated by a brake booster, a hydraulic unit intervening between a master cylinder and a wheel cylinder to control hydraulic pressure applied to the master cylinder, and a pipe for connecting the master cylinder with the hydraulic unit (for example see Patent Document 1).
In the brake system disclosed in the Patent Document 1, the pipe connecting for connecting the master cylinder with the hydraulic unit is constituted by a metal pipe, and a flexible hose made of a resin hose formed at the intermediate portion of the metal pipe and having an outer peripheral surface covered with a meshed metal wire. The flexible hose low in rigidity as compared with the metal pipe makes it possible for the shape of the pipe to finely be adjusted for the relative positional errors between the master cylinder and the hydraulic unit in assembling these parts. Further, the flexible hose can absorb vibrations to be transmitted from the hydraulic unit to the master cylinder.
There are some pipes which are to be used for the hydraulic system having the above brake system and the like, and are each constructed only by a resin pipe in consideration of the degree of freedom for the pipe to be mounted on the vehicle. One of the resin pipes to be used in the hydraulic system is shown for example in FIG. 13. The hydraulic system 100 shown in FIG. 13 comprises a resin pipe 103 incorporated therein. The resin pipe 103 intervenes between a hydraulic power unit 101 and a gear shift actuator 102, and is bent at a predetermined radius of curvature. The resin pipe 103 is clamped with and supported by a support member 105 at a desired position between the hydraulic power unit 101 and the gear shift actuator 102. The working oil outputted from the hydraulic power unit 101 is fed to the gear shift actuator 102 through a resin pipe 103.
The resin pipe 103 of this kind as shown in FIG. 13 is bent at the predetermined radius of curvature, and inclined toward a bent portion 103a from the hydraulic power unit 101 at a predetermined angle with respect to a horizontal plane, so that the resin pipe 103 is apt to vibrate up and down in response to the varied flowing motion of the working oil when the working oil passes through the resin pipe 103. At this time, the flowing motion of the working oil in the resin pipe 103 vibrating in this way causes what is called a Coriolis force F (F=2mωV, m: fluid mass, ω: fluid angular speed, V: fluid speed in the pipe) which acts in a direction perpendicular to the flowing direction of the working oil in the resin pipe 103. On the other hand, the resin pipe 103 is subject to a reaction force F′ against the Coriolis force F(N) from the support member 105. It is further known that the previously mentioned Coriolis force F is, as shown in FIG. 14, increased as the flow rate (ml/s) of the working oil flowing in the resin pipe 103 is increased, or otherwise the temperature (° C.) of the working oil is raised.
The Coriolis force F and the reaction force F′ acting on the resin pipe 103 are varied as the time elapses as clear from FIG. 15. The Coriolis force F and the reaction force F′ are, however, not equal to each other in magnitude although these forces are opposite in composition to each other. This means that in response to the time elapsed, the magnitude of the Coriolis force F exceeds the magnitude of the reaction force F′, or inversely the magnitude of the reaction force F′ exceeds the magnitude of the Coriolis force F. Here, for example, when the magnitude of the Coriolis force F exceeds the magnitude of the reaction force F′, the resin pipe 103 is brought into the state in which the resin pipe 103 is crushed. At this time, the working oil in the resin pipe 103 comes to be large in flow speed, while the hydraulic pressure of the working oil becomes more than the set value. It is thus to be noted that the resin pipe 103 shown in FIG. 13 designed without consideration of the balance between the Coriolis force F and the reaction force F′ results in one of the reasons for the hydraulic pressure to be prevented from being fed in a stable state.
On the other hand, the resin pipe 103 utilized in the hydraulic system 100 imparts the effects to the positional control and the responsive property of the hydraulic machine such as the gear shift actuator and the like irrespective of the resin pipe being wholly or partly made of resin when the rigidity of the pipe is varied in response to the temperature variation of the working oil passing through the resin pipe. For example, if the temperature of the working oil passing through the resin pipe 103 is raised, the rigidity of the resin pipe 103 tends to be decreased, thereby leading to the fact that the expansion amount of the resin pipe 103 what is called a hose compliance amount is increased. This results in the fact that the hydraulic pressure in the resin pipe 103 is decreased, thereby causing such a problem that the hydraulic machine such as the gear shift actuator 102 and the like among other things deteriorates in responsive property.
The rigidity variation of the resin pipe 103 stemming from the temperature variation of the working oil thus caused necessitates such a construction to make variable the control target value of the hydraulic machine such as the gear shift actuator and the like, which comes to be one of the causes to complex the control of the hydraulic pressure. Further, the abruptly lowering in rigidity of the resin pipe 103 possibly gives rise to vibrations in the hydraulic pressure.
It is therefore appreciated that the resin pipe 103 is therefore required to be subject to an appropriate hose compliance amount control.
The methods so far proposed to carry out the appropriate hose compliance amount control for the resin pipe include a method of introducing to the hydraulic system sensors, coolants, heat insulators, and an ECU (Electronic Control Unit) for executing a temperature environment control to perform the hose compliance amount control in the hard and soft aspects, and an additional method of using a metal pipe in lieu of the resin pipe or otherwise adding a metal blade or metal blades to the resin pipe.